Why boost-multi-index gives back a wrong iterator?
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28-06-2021 - |
题
Boost documents said that iterator_to gives back a valid iterator but the code below shows that something other happens.
All indices of Boost.MultiIndex provide a member function called iterator_to which returns an iterator to a given element of the container
http://www.boost.org/doc/libs/1_51_0/libs/multi_index/doc/tutorial/indices.html#iterator_to
#include <boost/multi_index_container.hpp>
#include <boost/multi_index/member.hpp>
#include <boost/multi_index/ordered_index.hpp>
#include <boost/multi_index/random_access_index.hpp>
using boost::multi_index_container;
using namespace boost::multi_index;
struct Test
{
int id;
std::string name;
};
struct idx{};
struct id{};
struct name{};
typedef boost::multi_index_container<
Test*,
indexed_by<
random_access<tag<idx> >,
ordered_unique<tag<id>, member<Test, int, &Test::id> >,
ordered_unique<tag<name>, member<Test, std::string, &Test::name> >
>
> TTestTable;
class TestTable : public TTestTable
{
public:
// Fill table with some values
TestTable()
{
Test* test1 = new Test();
Test* test2 = new Test();
Test* test3 = new Test();
Test* test4 = new Test();
test1->id = 1;
test2->id = 2;
test3->id = 3;
test4->id = 4;
test1->name = "name1";
test2->name = "name2";
test3->name = "name3";
test4->name = "name4";
push_back(test1);
push_back(test2);
push_back(test3);
std::cout << at(0)->name << std::endl;
std::cout << at(1)->name << std::endl;
std::cout << at(2)->name << std::endl;
typedef TTestTable::index<idx>::type test_table_by_index;
test_table_by_index::iterator it = get<0>().iterator_to(test1); // gives back a wrong iterator
std::cout << get<idx>().iterator_to(test1) - get<idx>().begin() << "\n"; // WRONG
replace(iterator_to(test1), test4); // CRASH
replace(it, rule4); // CRASH
}
};
int
main(int argc, char **argv)
{
TestTable table;
return 0;
}
解决方案
From the link you provided:
// The following, though similar to the previous code, // does not work: iterator_to accepts a reference to // the element in the container, not a copy. int x=c.back(); c.erase(c.iterator_to(x)); // run-time failure ensues
You're not passing a reference into iterator_to
, you're passing a copy.
The following should work:
Test* const& test1_ref = at(0);
typedef TTestTable::index<idx>::type test_table_by_index;
test_table_by_index::iterator it = get<0>().iterator_to(test1_ref);
std::cout << get<idx>().iterator_to(test1_ref) - get<idx>().begin() << "\n";
replace(iterator_to(test1_ref), test4);
As an aside, I don't think boost::multi_index_container
s are designed to be used as base classes since they don't provide a virtual destructor.
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